Etienne Jambon-Puillet - When walls are not smooth: wet ceilings and hairy pipes

Uneven solid surfaces are ubiquitous in Nature and can significantly impact fluid flow over them. In this presentation I will discuss two different configurations were the wall unevenness govern fluid transport.
First, I will consider wet ceilings. When liquid is coated on an upside-down surface, it destabilizes to form pendant drops surrounded by a thin film of liquid. I will show that these pendant drops ‘feel’ surface defects even though they have no contact line. The defects induce a gravito-capillary pinning-like force that can be harnessed to control the drop motion.
Second, I will consider hairy pipes. Many biological surfaces are covered with long and elastic filaments or ‘hairs’. I will show that when a fluidic channel is covered with hairs, the hydraulic resistance can become non-linear. This non-linearity is mediated by the hair flexibility and degree of channel obstruction and can be rationalized with a multi-scale model.